Abstract WP121: An Evaluation of Hemodynamics Across Intracranial Steno-occlusive Lesions by Computational Fluid Dynamics

Stroke ◽  
2016 ◽  
Vol 47 (suppl_1) ◽  
Author(s):  
Florence SY Fan ◽  
Vincent HL Ip ◽  
Alexander YL Lau ◽  
Anne YY Chan ◽  
Lisa WC Au ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Gradient ◽  
Pressure Difference ◽  
Pressure Ratio ◽  
Velocity Ratio ◽  
Strongly Correlated ◽  
Hemodynamic Parameters ◽  
Moderate Correlation ◽  
Anterior Circulation

Introduction: Intracranial atherosclerotic steno-occlusive disease (ICAS) is a major cause of stroke worldwide and portends a high risk of recurrence. Computational fluid dynamics (CFD) is a novel technique developed to solve and analyze the dynamic effects of fluid flow. We aimed to analyse hemodynamics across ICAS using CFD on processed CTA images and explore the correlation between the degree of arterial stenosis and hemodynamic flow status. Methods: We recruited patients with symptomatic ICAS from Acute Stroke Unit, Prince of Wales Hospital. All patients received CTA and DSA as vascular workup. Using CFD analysis of processed CTA images, we first defined the hemodynamic parameters, including pressure difference, pressure ratio, pressure gradient, shear strain rate ratio (SSR), wall shear stress (WSS) ratio and velocity ratio, across the stenosed vessels, and then we correlated the severity of stenosis as defined by DSA, with these parameters. Results: Among the 53 recruited patients (mean age 62.9 years, 69.8% males), 45 (85%) had lesions in the anterior circulation. The severity of stenosis showed a weak-to-moderate correlation with pressure difference (rs=0.392, p=0.004), pressure ratio (rs=-0.429, p=0.001) and pressure gradient (rs=0.419, p=0.002). There was no significant correlation between the severity of stenosis with SSR ratio, WSS ratio and velocity ratio. Among patients with anterior circulation stroke or TIA, the severity of stenosis showed a weak to moderate correlation with pressure difference (rs=0.381, p=0.01), pressure ratio (rs=-0.426, p=0.004) and pressure gradient (rs=0.407, p=0.005). For patients with posterior circulation stroke or TIA, the severity of stenosis was strongly correlated with pressure difference (rs=0.714, p=0.047) and pressure ratio (rs=-0.714, p=0.047); and very strongly correlated with velocity ratio (rs=0.833, p=0.01). Conclusions: The severity of ICAS showed only weak-to-moderate correlation with hemodynamic parameters across the culprit lesion. Thus, risk stratification and treatment based solely on stenotic severity may be inadequate. Our findings may guide further research in estimating stroke risks and selection of high-risk patients who may benefit from adjunctive treatments.

scholarly journals Translesional Pressure Gradient Alters Relationship Between Blood Pressure and Recurrent Stroke in Intracranial Stenosis

Stroke ◽  
2020 ◽  
Vol 51 (6) ◽  
pp. 1862-1864
Author(s):  
Xueyan Feng ◽  
Ka Lung Chan ◽  
Linfang Lan ◽  
Jill Abrigo ◽  
Vincent H.L. Ip ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computed Tomography ◽  
Blood Pressure ◽  
Computational Fluid Dynamics ◽  
Pressure Gradient ◽  
Primary Outcome ◽  
Recurrent Stroke ◽  
Pressure Ratio ◽  
Increased Risk ◽  
Dynamics Models

Background and Purpose— There is debate over an optimal systolic blood pressure (SBP) in secondary stroke prevention of patients with symptomatic intracranial atherosclerotic stenosis (sICAS). We investigated whether translesional pressure gradient across sICAS would alter the relationship between SBP and risk of recurrent stroke in such patients. Methods— We recruited patients with sICAS (50%–99% stenosis) confirmed in computed tomography angiography. We simulated blood flow across sICAS with computed tomography angiography-based computational fluid dynamics models. Translesional pressure ratio (PR=Pressure post-stenotic /Pressure pre-stenotic ) was calculated in each case. Pressure ratio (PR) ≤ median was defined as low PR, indicating larger translesional pressure gradient across sICAS. All patients received optimal medical treatment. We investigated the interaction of translesional PR and mean SBP during follow-up (SBP FU ) in determining the risk of the primary outcome, recurrent ischemic stroke in the same territory within 1 year. Results— Among 157 patients with sICAS, the median PR was 0.93. Multivariate Cox regression revealed significant PR-SBP FU interaction on the primary outcome ( P =0.008): in patients with normal PR, risk of primary outcome significantly decreased with lower SBP FU (hazard ratio for 10 mm Hg decrement =0.46; P =0.018); however, in those with low PR, SBP FU ≤130 mm Hg was associated with significantly increased risk of primary outcome, compared with 130<SBP FU <150 mm Hg (hazard ratio=5.08; P =0.043). Conclusions— Low SBP level may be associated with increased risk of stroke recurrence in patients with sICAS with a large translesional pressure gradient. Translesional PR by computational fluid dynamics models may yield a promising indicator to guide more individualized blood pressure management in patients with sICAS, warranting future studies.

scholarly journals The Hydrodynamics and Mixing Performance in a Moving Baffle Oscillatory Baffled Reactor through Computational Fluid Dynamics (CFD)

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1236
Author(s):  
Hamid Mortazavi ◽  
Leila Pakzad
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Dispersion Coefficient ◽  
Velocity Ratio ◽  
Axial Dispersion ◽  
Shear Strain Rate ◽  
Turbulent Length Scale ◽  
Mixing Performance ◽  
Axial Dispersion Coefficient ◽  
Computational Fluid Dynamics Cfd

Oscillatory baffled reactors (OBRs) have attracted much attention from researchers and industries alike due to their proven advantages in mixing, scale-up, and cost-effectiveness over conventional stirred tank reactors (STRs). This study quantitatively investigated how different mixing indices describe the mixing performance of a moving baffle OBR using computational fluid dynamics (CFD). In addition, the hydrodynamic behavior of the reactor was studied, considering parameters such as the Q-criterion, shear strain rate, and velocity vector. A modification of the Q-criterion showed advantages over the original Q-criterion in determination of the vortices’ locations. The dynamic mesh tool was utilized to simulate the moving baffles through ANSYS/Fluent. The mixing indices studied were the velocity ratio, turbulent length scale, turbulent time scale, mixing time, and axial dispersion coefficient. We found that the oscillation amplitude had the most significant impact on these indices. In contrast, the oscillatory Reynolds number did not necessarily describe the mixing intensity of a system. Of the tested indices, the axial dispersion coefficient showed advantages over the other indices for quantifying the mixing performance of a moving baffle OBR.

The Application of Non-Axisymmetric Endwall Contouring in a Single Stage, Rotating Turbine

2009 ◽  
Author(s):  
Glen Snedden ◽  
Dwain Dunn ◽  
Grant Ingram ◽  
David Gregory-Smith
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Gradient ◽  
Full Scale ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Detailed Understanding ◽  
Low Speed ◽  
Endwall Contouring ◽  
Probe Measurements

As turbine manufacturers strive to develop machines that are more efficient, one area of focus has been the control of secondary flows. To a large extent these methods have been developed through the use of computational fluid dynamics and detailed measurements in linear and annular cascades and proven in full scale engine tests. This study utilises 5-hole probe measurements in a low speed, model turbine in conjunction with computational fluid dynamics to gain a more detailed understanding of the influence of a generic endwall design on the structure of secondary flows within the rotor. This work is aimed at understanding the influence of such endwalls on the structure of secondary flows in the presence of inlet skew, unsteadiness and rotational forces. Results indicate a 0.4% improvement in rotor efficiency as a result of the application of the generic non-axisymmetric endwall contouring. CFD results indicate a clear weakening of the cross passage pressure gradient, but there are also indications that custom endwalls could further improve the gains. Evidence of the influence of endwall contouring on tip clearance flows is also presented.

Effect of Cavities in Suddenly Expanded Flow at Supersonic Mach Number

CFD letters ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 57-71
Author(s):  
Atifatul Ismah Ismail
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Mach Number ◽  
Pressure Ratio ◽  
Area Ratio ◽  
Base Pressure ◽  
Sudden Expansion ◽  
Expansion Level ◽  
Computational Fluid Dynamics Cfd ◽  
Base Drag

The contribution from the base drag due to the sub-atmospheric pressure is significant. It can be more than two-thirds of the net drag. There is a need to increase the base pressure and hence decrease the base drag. This research examines the effect of Mach Number on base pressure. To accomplish this objective, it controls the efficacy in an enlarged duct computed by the numerical approach using Computational Fluid Dynamics (CFD) Analysis. This experiment was carried out by considering the expansion level and the aspect cavity ratio. The computational fluid dynamics method is used to model supersonic motion with the sudden expansion, and a convergent-divergent nozzle is used. The Mach number is 1.74 for the present study, and the area ratio is 2.56. The L/D ratio varied from 2, 4, 6, 8, and 10, and the simulated nozzle pressure ratio ranged from 3 to 11. The two-dimensional planar design used commercial software from ANSYS. The airflow from a Mach 1.74 convergent-divergent axi-symmetric nozzle expanded suddenly into circular ducts of diameters 17 and 24.5 mm with and without annular rectangular cavities. The diameter of the duct is taken D=17mm and D=24.5mm. The C-D nozzle was developed and modeled in the present study: K-ε standard wall function turbulence model was used with the commercial computational fluid dynamics (CFD) and validated. The result indicates that the base pressure is impacted by the expansion level, the enlarged duct size, and the passage’s area ratio.

scholarly journals A zonal approach for estimating pressure ratio at compressor extreme off-design conditions

2018 ◽  
Vol 20 (4) ◽  
pp. 393-404 ◽  
Author(s):  
José Galindo ◽  
Roberto Navarro ◽  
Luis Miguel García-Cuevas ◽  
Daniel Tarí ◽  
Hadi Tartoussi ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Speed ◽  
Internal Combustion Engines ◽  
Pressure Ratio ◽  
Internal Combustion ◽  
Operating Conditions ◽  
Combustion Engines ◽  
One Dimensional ◽  
Performance Map

Zero-dimensional/one-dimensional computational fluid dynamics codes are used to simulate the performance of complete internal combustion engines. In such codes, the operation of a turbocharger compressor is usually addressed employing its performance map. However, simulation of engine transients may drive the compressor to work at operating conditions outside the region provided by the manufacturer map. Therefore, a method is required to extrapolate the performance map to extended off-design conditions. This work examines several extrapolating methods at the different off-design regions, namely, low-pressure ratio zone, low-speed zone and high-speed zone. The accuracy of the methods is assessed with the aid of compressor extreme off-design measurements. In this way, the best method is selected for each region and the manufacturer map is used in design conditions, resulting in a zonal extrapolating approach aiming to preserve accuracy. The transitions between extrapolated zones are corrected, avoiding discontinuities and instabilities.

Computational Fluid Dynamics Study of Oil Behavior in a Scoop, and Factors Affecting Scoop Capture Efficiency

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Evgenia Korsukova ◽  
Hervé Morvan
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Gas Turbines ◽  
High Speed ◽  
Velocity Ratio ◽  
Capture Efficiency ◽  
Parameter Analysis ◽  
Parameter Study ◽  
3D Simulations ◽  
Engine Components

Abstract Due to the continuous reduction of engine sizes, efficient under-race lubrication becomes ever more crucial in order to provide sufficient amount of oil to various engine components. An oil scoop is a rotating component that captures oil from a jet, and axially redirects it to the bearing, providing under-race lubrication. Given the importance of lubrication in high-speed engine components, the efficiency study of under-race lubrication appliances receives rapidly growing demands from manufacturers and therefore is of great interest. This work provides description of computational fluid dynamics (CFD) methods that were found to be most accurate and efficient for a large parameter analysis of the scoop capture efficiencies. One of the main purposes of this paper is to demonstrate an optimal and validated computational approach to modeling under-race lubrication with a focus on oil capture efficiency. Second, to show which factors most influence the scoop capture efficiency. Additionally, simulations allow for the fluid behavior inside the scoop to be observed that cannot be visualized experimentally due to high speeds. An improved method of efficiency calculation is also presented and compared to existing methods (Cageao, P. P., Simmons, K., Prabhakar, A., and Chandra, B., 2019, “Assessment of the Oil Scoop Capture Efficiency in High Speed Rotors,” ASME J. Eng. Gas Turbines Power, 141(1), p. 012401; Korsukova, E., Kruisbrink, A., Morvan, H., Paleo Cageao, P., and Simmons, K., 2016, “Oil Scoop Simulation and Analysis Using CFD and SPH,” ASME Paper No. GT2016-57554.). Results of both two-dimensional (2D) and semi-three-dimensional (3D) simulations are provided. Both qualitative comparison of 2D with semi-3D simulations and quantitative comparison of 2D simulations with experiments (Cageao, P. P., Simmons, K., Prabhakar, A., and Chandra, B., 2019, “Assessment of the Oil Scoop Capture Efficiency in High Speed Rotors,” ASME J. Eng. Gas Turbines Power, 141(1), p. 012401) show consistency. Parameter study using 2D simulations is shown with variation of rotational scoop speed, jet angles, velocity ratio. Key results show that changes of the jet angle and velocity ratio can improve the scoop efficiency.

Computational Fluid Dynamics Investigation of Brush Seal Leakage Performance Depending on Geometric Dimensions and Operating Conditions

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Yahya Dogu ◽  
Ahmet S. Bahar ◽  
Mustafa C. Sertçakan ◽  
Altuğ Pişkin ◽  
Ercan Arıcan ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Ratio ◽  
Plate Thickness ◽  
Operating Conditions ◽  
Design Parameters ◽  
Backing Plate ◽  
Brush Seal ◽  
Front Plate ◽  
Brush Seals

Brush seals require custom design and tailoring due to their behavior driven by flow dynamic, which has many interacting design parameters, as well as their location in challenging regions of turbomachinery. Therefore, brush seal technology has not reached a conventional level across the board standard. However, brush seal geometry generally has a somewhat consistent form. Since this consistent form does exist, knowledge of the leakage performance of brush seals depending on specific geometric dimensions and operating conditions is critical and predictable information in the design phase. However, even though there are common facts for some geometric dimensions available to designers, open literature has inadequate quantified information about the effect of brush seal geometric dimensions on leakage. This paper presents a detailed computational fluid dynamics (CFD) investigation quantifying the leakage values for some geometric variables of common brush seal forms functioning in some operating conditions. Analyzed parameters are grouped as follows: axial dimensions, radial dimensions, and operating conditions. The axial dimensions and their ranges are front plate thickness (z1 = 0.040–0.150 in.), distance between front plate and bristle pack (z2 = 0.010–0.050 in.), bristle pack thickness (z3 = 0.020–0.100 in.), and backing plate thickness (z4 = 0.040–0.150 in.). The radial dimensions are backing plate fence height (r1 = 0.020–0.100 in.), front plate fence height (r2 = 0.060–0.400 in.), and bristle free height (r3 = 0.300–0.500 in.). The operating conditions are chosen as clearance (r0 = 0.000–0.020 in.), pressure ratio (Rp = 1.5–3.5), and rotor speed (n = 0–40 krpm). CFD analysis was carried out by employing compressible turbulent flow in 2D axisymmetric coordinate system. The bristle pack was treated as a porous medium for which flow resistance coefficients were calibrated by using literature based test data. Selected dimensional and operational parameters for a common brush seal form were investigated, and their effects on leakage performance were quantified. CFD results show that, in terms of leakage, the dominant geometric dimensions were found to be the bristle pack thickness and the backing plate fence height. It is also clear that physical clearance dominates leakage performance, when compared to the effects of other geometric dimensions. The effects of other parameters on brush seal leakage were also analyzed in a comparative manner.

Numerical Simulations of the Non-Newtonian Blood Blow in Human Abdominal Artery Based on Reverse Engineering

2011 ◽  
Vol 140 ◽  
pp. 195-199 ◽  
Author(s):  
Jin You YANG ◽  
Yang Hong
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Blood Flow ◽  
Fluid Flow ◽  
Reverse Engineering ◽  
Power Law ◽  
Cardiac Cycle ◽  
Hemodynamic Parameters ◽  
Human Artery ◽  
Computational Fluid Dynamics Cfd

The method that combined the reverse engineering based on CT medical images and computational fluid dynamics (CFD) was used to perform simulation the Non-Newtonian blood fluid flow in human abdominal artery, then analyzed the hemodynamic condition about the bifurcation of human abdominal artery. A Non-Newtonian blood model (the Generalised Power Law) was used to study the hemodynamic parameters during entire cardiac cycle. Calculated results for the Non-Newtonian blood flow show us the methods performed in this study is suitable for numerical simulating the blood flow in human artery and investigating the relation between hemodynamic factors and vascular disease.

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